The show dogs behaving (very) badly did a show on this, puppy who only went inside.
They went outside with the puppy and sat on the bench (in warm coats with large mugs of coffee) and they waited, and waited and waited.
First wee took over an hour. As soon as they were weeing, they were full of praise and rewards.
Stayed outside. 20 minutes later, next wee. Loads of praise.
20 minutes later a poo and loads of praise.
Then they went inside and no wee. half and hour later came out, and puppy weed straight away.
I know it is edited etc, but I thought it was interesting that they just sat outside, not for one wee, but until he had done several.